Keratoconus (KC) is a potentially binding disease that thins and scars the central corneal stroma. The findings of recent studies on the biochemistry of human corneas are beginning to elucidate the basic biologic defects of KC. This research program examines a number of compelling hypotheses regarding the cellular and molecular aberrations that differentiate the KC from the normal human corneas: 1) KC corneas contain a reduced amount of total protein. The reduction may be related to an abnormal degradation of corneal proteins. To verify further and to elucidate the dynamics of the degradation processes the levels of prote ases (including cathepsins B, D, and G, elastase, gelatinase, collagenase, and plasminogen activator), and inhibitors (including alpha-1-proteinase inhibitor and alpha-2-macroglobulin) will be measured in KC and control (including those from age-similar normal subject and patients with other corneal diseases) corneas. Enzymatic assays, gel electrophoresis, and enzyme-linked immunosorbent and dot blot assays will be performed. Data from the epithelial, stromal, and endothelial layers of KC and control corneal tissues will be compared. 2) The corneal epithelium per se. or its interaction with the stroma, may play a role in KC. An in vitro co- culture system will be used to explore the interactions of these two cell types. Co-culture will be set up with normal human corneal stromal cells plus KC or normal human corneal epithelial cells maintained on a Millicell-CM Biopore membrane insert. The assayed levels of lysosomal cathepsins and other enzymes in each cell type in the co-culture system will be compared with those in cells grown separately, to determine whether the KC epithelial cells can induce the stromal cells to produce degradative enzymes to a higher level than those from controls. 3) KC corneas possess a higher-than-normal amount of glycoconjugates. Lectin probes will be used to examine further the nature and quantity of specific groups of glycoconjugate molecules in KC and control corneas. Also, the quantity and biochemical characteristics, such as the molecular size and degree of sulfation, of proteoglycans in KC corneas will be analyzed by immunologic and biochemical methods and compared with those of controls. 4) Collagen content in the cornea is reduced in some, but not in all KC cases. The molecular basis for this alteration will be studies using specific nucleic acid probes to collagen types I, III, and V. In situ hybridization, Northern blot, and dot blot assays will be performed to determine the collagen mRNA levels in both groups of KC corneas and in controls, and to reveal the alteration sites.